Monoclonal antibodies reactive with various human tumor cells have been prepared from murine hybridomas according to standard techniques. Such antibodies have previously been administered to man by other investigators in limited Phase I trials and have been shown to be without serious toxicities and have occasional objective evidence of antitumor effect. Phase I trials of antitumor monoclonal antibodies initiated by the Clinical Investigations Section include studies of anti-T cell monoclonal antibodies in patients with chronic lymphocytic leukemia and cutaneous T cell lymphoma, anti-melanoma monoclonal antibody in patients with disseminated melanoma, and anti-idiotype monoclonal antibody in patients with refractory malignant lymphoma.